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A least-squares (LS) channel estimation (CE) technique for mobile orthogonal frequency-division multiplexing (OFDM) communications over a rapidly time-varying frequency-selective fading channel is investigated in this paper. The proposed technique keeping the comb-type pilot arrangement can achieve a low error probability by accurately estimating channel impulse response (CIR) and effectively tracking rapid CIR time variations. The LS CE technique proposed here is conducted in the time domain (TD). Meanwhile, a generic estimator is serially performed block by block without assistance from a priori channel information and without increasing computational complexity. By taking advantage of linearly frequency-modulated (LFM) or pseudorandom signals transceived for jointly sounding pilot subchannels, the proposed LS CE can inherently perform pseudonoise (PN) matched filtering (MF) to suppress multipath interference (MPI) caused by frequency-selective fading and intercarrier interference (ICI) resulting from data subchannels. The optimality of the proposed technique is verified by taking Cramer-Rao lower bounds (CRLBs) into comparison both on noise- and interference-dominant signal-to-noise ratio (SNR) conditions. In addition, the dual optimality of the LFM and PN pilot symbols is verified for both TD and frequency-domain (FD) CEs. Furthermore, the proposed technique also exhibits good resistance against residual timing errors occurring with the discrete Fourier transform (DFT) demodulation. Extensive computer simulations in conjunction with statistical derivations show the superiority of the proposed technique.
Date of Publication: Nov. 2008